It is well known in the art to utilize developing agents to insolubilize colloidal materials, such as gelatin, in a silver halide emulsion. Typically, in the employment of this hardening reaction, a tanning developing agent is utilized to develop an exposed silver halide colloidal emulsion and crosslink the molecules of the emulsion, i.e., harden the emulsion, after which the unexposed areas may be washed away utilizing warm water, to thereby provide a photographic image or resist of the hardened or tanned colloidal material.
During processing, the oxidation products of the developing agents which are formed in the exposed regions of the image diffuse through the gelatin layers containing same, hardening the colloidal gelatin itself. Accurate, i.e., imagewise, tanning development requires that the oxidation products of the developing agents which are produced by the reduction of the silver image and harden the gelatin remain in close proximity to the reduced silver image. The desired low mobility of these oxidation products necessitates their low solubility in the developer solution, a function of their minimal interaction with the components of that solution.
Such photographic emulsion layers typically may contain colorants, e.g., pigments, carbon black, etc., which may impart color to the thus formed images. Literature examples of such photographic elements include those described in U.S. Pat. Nos. 3,364,024; 2,837,430; 4,283,479; 4,299,909; 4,233,392; 4,233,393; 4,254,210; and G.B. Pat. No. 2,026,186A.
Tanning developer solutions typically used for such photographic elements are simple aqueous solutions which contain therein a high content of sulfate salts, wherein the tanning developing agents themselves may be incorporated within the gelatin layers of the silver halide emulsion-containing article.
In conventional photographic silver halide systems, antioxidants such as sulfites are commonly utilized during development. Conventional photographic developers reduce a latent silver image to a black silver image. The oxidation products of the developing agents must be sufficiently soluble in the developing solution that they will be completely washed out of the gelatin matrix. Incomplete removal of the oxidation products may result in undesirable background staining and coloring. Therefore conventional photographic developer solutions typically contain substantial amounts of sulfite salts to enhance the solubility of the oxidation products. Furthermore, sulfites also act as preservatives and antioxidants which retard the aerial oxidation of the developing agents.
In a tanning developer system, the developer solution is, however, typically devoid of common antioxidants such as sulfite salts, or contains a reduced level thereof, due to their harmful effect on the tanning process, as is described in C. E. K. Mees and T. H. James, The Theory Of The Photographic Process, 3rd Edition, the McMillan Co., 1966, at page 304. Even small quantities, i.e., two to three grams per liter, of an antioxidant such as sodium sulfite may limit or destroy the tanning action. (G. M. Haist, Modern Photographic Processing, Wiley and Sons, 1979 at page 512.)
As a result, the image processing step of tanning development is susceptible to air oxidation, which can display itself through the non-imagewise hardening of the gelatin layers when the photographic element is exposed to air while wet with the developing solution.
To attempt to combat this problem, the literature has reported the use of materials such as ascorbic acid as an antioxidant, as described in GB Pat. No. 560,371 and U.S. Pat. No. 2,415,666, and ascorbic acid borates as described in U.S. Pat. No. 2,967,772.
Conversely, U.S. Pat. No. 3,293,035 discloses the use of primary amines and monohydroxy aromatic compounds, themselves not being developing agents, to improve selective tanning only in image areas, while U.S. Pat. No. 2,404,774 details the use of urea as a softening agent for gelatin coatings. Nitrile compounds are further cited as stabilizing agents for graphic arts developing solutions; e.g., U.S. Pat. No. 3,772,022.
Hydroxylamine derivatives have been taught to supplement the stability of color developer solutions, as for example in U.S. Pat. Nos. 3,746,544; 4,155,763; 4,055,426; and 4,170,478. Alkanolamines and their derivatives are taught to be well known as pH regulators in the area of graphic arts developer solutions, see for example, U.S. Pat. No. 3,984,243. Furthermore, in the area of dye-forming developers, the use of hydroxylamines together with alkanolamines has been taught to enhance the stability of such developing solutions, see for example GB Pat. Nos. 2,060,921B and 2,075,496B and EPO Pat. No. 47781.
Present developer solutions, however, do not provide adequate protection from the oxidation effects of air as displayed by non-imagewise hardening.
Also, known developer solutions have a narrow temperature latitude in which they function, i.e., either only at high temperatures or low temperatures. Low temperature developers are generally slow, requiring extended residence time in the developing solution, thereby increasing susceptibility to oxidation from the air. High temperature developers accelerate image development and the effects of oxidation.
The oxidation manifests itself as non-imagewise hardening, which affects final image quality, e.g., half-dot retention is very narrow because the 90 percent dots are clogged and the 5 percent dots too large.